1. Field of the Invention
The present invention relates to a control system for a adjustable damping force, which controls variably an adjustable damping force of a damper provided to a suspension apparatus of a vehicle in response to a moving condition of the vehicle.
2. Description of the Background Art
In Japanese Patent Unexamined Publication No. JP-A-60-113711, the adjustable damping force in which MRF (Magneto-Rheological Fluids), whose viscosity is changed by applying a magnetic field, is employed as a viscous fluid of the adjustable damping force for the suspension apparatus and also a coil used to apply the magnetic field to the magneto-rheological fluids in the fluid passage is provided to a piston, which is slidably fitted into a cylinder, is known. According to this adjustable damping force, an damping force of this damper can be controlled arbitrarily by changing a viscosity of the magneto-rheological fluids in the fluid passage by applying the magnetic field generated by supplying an electric current to the coil.
An damping force generated by a adjustable damping force set forth in Japanese Patent Unexamined Publication No. JP-A-60-113711 is changed by a current supplied to a coil of the damper. When the driving stability control to suppress a rolling and a pitching of the vehicle by changing an damping force of the damper is to be carried out, a target damping force that is proportional to a rate of change in a lateral acceleration and a rate of change in a longitudinal acceleration of the vehicle sensed by a sensor with respect to time is calculated. Then, a current value to be supplied to the coil of the damper is searched from a map using this target damping force and a damper speed as parameters.
Meanwhile, it is inevitable that the noise is superposed on outputs of the sensors that sense the lateral acceleration and the longitudinal acceleration of the vehicle to calculate the target damping force of the damper. When the output of the sensor is large, an occupied rate of noise is small and the influence of noise is negligible. But an output itself of the sensor is small when the vehicle goes straight on at a constant speed, a occupied rate of noise in the sensor output is increased. In this manner, when a sensing precision of the lateral acceleration and the longitudinal acceleration sensed by the sensors is lowered by the noise, it is possible that a precision of the target damping force of the damper is lowered and then the driving stability control cannot be exactly executed.